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How to set up your new CentOS 7 server

August 15, 2017, Written by 0 comment

So you have a fresh new server, now what?

There are a few configuration steps you’ll need to go through before you can start playing around with your new kit. This is for security and makes your life a lot easier.

Step 1 – Root Login

You’ll need to ssh in to your server using your root login credentials.

You can use an SSH tool such as PuTTY.

Connect to your server’s public IP address and log in using your root account.

Complete the login process by accepting the warning about host authenticity, if it appears, then providing your root authentication (password or private key). If it is your first time logging into the server, with a password, you will also be prompted to change the root password.

What is a Root user?

The root user is the administrative user in a Linux environment that has very broad privileges. Because of the heightened privileges of the root account, you are actually discouraged from using it on a regular basis. This is because part of the power inherent with the root account is the ability to make very destructive changes, even by accident.

The next step is to set up an alternative user account with a reduced scope of influence for day-to-day work.

Step 2 — Create a New User

Once you are logged in as root, we’re prepared to add the new user account that we will use to log in from now on.

This example creates a new user called “demo”, but you should replace it with a user name that you like:
adduser demo
Next, assign a password to the new user (again, substitute “demo” with the user that you just created):
passwddemo

Note: use a strong password, don’t forget to write it down somewhere safe.

More details on adding and removing users can be found in this guide.

Step 3— Root Privileges

Now, we have a new user account with regular account privileges. However, we may sometimes need to do administrative tasks.

To avoid having to log out of our normal user and log back in as the root account, we can set up what is known as “super user” or root privileges for our normal account. This will allow our normal user to run commands with administrative privileges by putting the word sudo before each command.

To add these privileges to our new user, we need to add the new user to the “wheel” group. By default, on CentOS 7, users who belong to the “wheel” group are allowed to use the sudo command.

As root, run this command to add your new user to the wheel group (substitute the highlighted word with your new user):
gpasswd -a demo wheel
Your user can now run commands with super user privileges. See this guide on what that means.

The next step in securing your server is to set up public key authentication for your new user. Setting this up will increase the security of your server by requiring a private SSH key to log in.

Generate a Key Pair

If you do not already have an SSH key pair, which consists of a public and private key, you need to generate one. If you already have a key that you want to use, skip to the Copy the Public Key step.

To generate a new key pair, enter the following command at the terminal of your local machine:
ssh-keygen
Assuming your local user is called “localuser”, you will see output that looks like the following:
Generating public/private rsa key pair.
Enter file in which to save the key (/Users/localuser/.ssh/id_rsa):

Hit return to accept this file name and path (or enter a new name).

Next, you will be prompted for a passphrase to secure the key with. You may either enter a passphrase or leave the passphrase blank.

Note: If you leave the passphrase blank, you will be able to use the private key for authentication without entering a passphrase. If you enter a passphrase, you will need both the private key and the passphrase to log in. Securing your keys with passphrases is more secure, but both methods have their uses and are more secure than basic password authentication.

This generates a private key, id_rsa, and a public key, id_rsa.pub, in the .ssh directory of the localuser’s home directory. Remember that the private key should not be shared with anyone who should not have access to your servers!

Copy the Public Key

After generating an SSH key pair, you will want to copy your public key to your new server. We will cover two easy ways to do this.

Option 1: Use ssh-copy-id

If your local machine has the ssh-copy-id script installed, you can use it to install your public key to any user that you have login credentials for.

Run the ssh-copy-id script by specifying the user and IP address of the server that you want to install the key on, like this:
ssh-copy-id demo@SERVER_IP_ADDRESS

After providing your password at the prompt, your public key will be added to the remote user’s .ssh/authorized_keys file. The corresponding private key can now be used to log into the server.

Option 2: Manually Install the Key

Assuming you generated an SSH key pair using the previous step, use the following command at the terminal of your local machine to print your public key (id_rsa_pub):
cat ~/.ssh/id_rsa.pub
This should print your public SSH key, which should look something like the following:
ssh-rsa aaaa......aaaaaaaS/1rggpFmu3HbXBnWSUdf localuser@machine.local

Select the public key, and copy it to your clipboard.

Add Public Key to New Remote User

To enable the use of SSH key to authenticate as the new remote user, you must add the public key to a special file in the user’s home directory.

On the server, as the root user, enter the following command to switch to the new user (substitute your own user name):
su - demo
Now you will be in your new user’s home directory.

Create a new directory called .ssh and restrict its permissions with the following commands:
mkdir .ssh
chmod 700 .ssh

Now open a file in .ssh called authorized_keys with a text editor. We will use vi to edit the file:
vi .ssh/authorized_keys
Enter insert mode, by pressing i, then enter your public key (which should be in your clipboard) by pasting it into the editor. Now hit ESC to leave insert mode.

Enter
:x
then ENTER to save and exit the file.

Now restrict the permissions of the authorized_keys file with this command:
chmod 600 .ssh/authorized_keys
Type this command once to return to the root user:
exit
Now you may SSH login as your new user, using the private key as authentication.
Want to know how authentication works? See this article.

Step 5— Configure SSH Daemon

Now that you have your new account, you can secure your server a little bit by modifying its SSH daemon configuration (the program that allows us to log in remotely) to disallow remote SSH access to the root account.

Begin by opening the configuration file with your text editor as root:
vi /etc/ssh/sshd_config
Here, we have the option to disable root login through SSH. This is generally a more secure setting since we can now access our server through our normal user account and escalate privileges when necessary.

To disable remote root logins, we need to find the line that looks like this:
#PermitRootLogin yes
Hint: To search for this line, type /PermitRoot then hit ENTER. This should bring the cursor to the “P” character on that line.

Uncomment the line by deleting the “#” symbol (press Shift-x).

Now move the cursor to the “yes” by pressing c.

Now replace “yes” by pressing cw, then typing in “no”. Hit Escape when you are done editing. It should look like this:
PermitRootLogin no
Disabling remote root login is highly recommended on every server!

Enter:
:x
then ENTER to save and exit the file.

Reload SSH

Now that we have made our changes, we need to restart the SSH service so that it will use our new configuration.

Type this to restart SSH:
systemctl reload sshd
Now, before we log out of the server, we should test our new configuration. We do not want to disconnect until we can confirm that new connections can be established successfully.

Open a new terminal window. In the new window, we need to begin a new connection to our server. This time, instead of using the root account, we want to use the new account that we created.

For the server that we configured above, connect using this command. Substitute your own information where it is appropriate:
ssh demo@SERVER_IP_ADDRESS
Note: As you are using PuTTY to connect to your servers, be sure to update the session’s port number to match your server’s current configuration.

You will be prompted for the new user’s password that you configured. After that, you will be logged in as your new user.

Remember, if you need to run a command with root privileges, type “sudo” before it like this:
sudo command_to_run

If all is well, you can exit your sessions by typing:
exit

All done!

 

Original Content by Mitchell Anicas and edited by the author of this post according to the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

Ian Ensor